noun

• (archaic) The quality or fact of being ancient or very old.
  "PEN, made of reed, cut, &c. like our pens, is of classical ancientry; but the first certain account of quill pens is in 636, in Isidore."
• (archaic) Old-fashioned style, elaborate ceremony.
  "[…] wooing, wedding, and repenting, is as a Scotch jig, a measure, and a cinque pace: the first suit is hot and hasty, like a Scotch jig, and full as fantastical; the wedding, mannerly-modest, as a measure, full of state and ancientry; and then comes repentance and, with his bad legs, falls into the cinque pace faster and faster, till he sink into his grave."
• (archaic) Elderly people, elders, ancients (collectively).
  "I would there were no age between sixteen and three-and-twenty, or that youth would sleep out the rest; for there is nothing in the between but getting wenches with child, wronging the ancientry, stealing, fighting—"
• (archaic) Something ancient (countable); ancient things (collectively).
  "Kings Lynn is a pleasant town to ramble about. […] In its quiet and more secluded streets you come upon bits of ancientry, the waifs and strays of monastic times […]"